Underground conduits are widely used for the transmission of fluids, such as in pipelines and the like, as well as for carrying wires and cables for the transmission of electrical power and electrical communication signals. While the installation of such conduits is time-consuming and costly for locations where the earth can be excavated from the surface, routing of such conduits becomes more difficult where surface excavation cannot be performed due to the presence of surface obstacles through which the excavation cannot easily precede. Such surface obstacles include highways and railroads and rivers.
A method for installing underground conduits is disclosed in U.S. Pat. No. 4,679,673, issued Jul. 14, 1987, assigned to Cherrington Corporation, which is incorporated by reference herein. This patent discloses a method of forming an enlarged arcuate bore and installing a conduit therein, beginning with the directional drilling of a pilot hole between surface locations and under a surface obstacle, such as a river. Following the drilling of the pilot hole, a reamer is pulled with the pilot drill string from the exit opening toward the entry opening in order to enlarge the pilot hole to a size which will accept the conduit or pipe.
Inserting the pipe in the bore hole can be problematic. The pipeline is pulled through the bore hole using a drill string; however, the pipe can lodge into the sides of the bore hole or into a bore hole full of cuttings to an extent that the drill string cannot provide sufficient power to free the pipeline. In such cases, additional impetus must be provided to the pipeline to dislodge it.
FIG. 1 illustrates a previously used method for forcing a pipeline 10 into a bore hole 12. A collar 14 is secured to the pipeline 10. A tractor 16 having a winch 18 is coupled to the collar over cable 20. By pulling cable 20 with winch 18, the pipeline 10 is pulled toward bore hole 12.
Although the method shown in connection with FIG. 1 has been used successfully, a serious problem with this method is the direction in which the pipeline 10 is pulled. Since the pipeline 10 is pulled at an angle toward tractor 16, the pipeline 10 may be driven toward the walls of the bore hole 12, rather than directly down the axis of the hole. Thus, while the method of FIG. 1 generates the desired forward thrust, it also generates an additional undesirable lateral force. This problem can be somewhat alleviated by using two tractors, one on either side of the pipeline 10, to offset the lateral force components. However, in practice, it is difficult to exactly offset the forces, and therefore, undesirable lateral forces which drive the pipe into the sidewalls of the bore hole 12 remain.
Another method to provide impetus to the pipeline 10 is shown in FIG. 2. This method is similar to that shown in FIG. 1, with the addition of a sheave 22 coupled to collar 14 and a deadman 24 mounted in the ground. Cable 20 is routed around sheave 22 and attached to deadman 24. Again, as the cable 20 is retracted onto winch 18, a force is applied to pipeline 10 driving it into the bore hole 12. Use of the sheaves 22 is advantageous because of the multiple forces applied to the pipeline. However, this arrangement suffers from the same problem as the method of FIG. 1, since lateral forces which pull the pipeline 10 toward the sidewalls of the bore hole 12 are created. Further, it is difficult to control or balance two or more power units for a uniform pull on the pipeline 10.
FIG. 3 illustrates a third method for providing thrust to a pipeline 10. In this method, a tractor 16 with a crane 26 is used to drive the pipeline 10 into the bore hole 12. From this view, it can be seen that the drill string 28, which is coupled to the pipeline 10, is also used to pull the pipeline 10 into the bore hole 12. While this method for driving the pipeline 10 can be used to reduce the angle at which the force is applied, thereby reducing the lateral forces on the pipeline 10, the stability of the tractor 16 with the crane 26 is attached, thereby reducing the force which may be applied to the pipeline 10.
Therefore, a need has arisen in the industry for an improved method and apparatus for thrusting a pipeline into a bore hole.